Getting all 3 Horse Power out of your GT-5 Sky? (tear down)

Discussion in 'Motorized Bicycle General Discussion' started by recon chris, Jan 19, 2012.

  1. recon chris

    recon chris New Member

    Joined:
    Apr 28, 2011
    Messages:
    87
    Likes Received:
    0
    Thanks dmb I might do a reed job as an after build performance modification. It makes allot of sense but it’s not on the agenda due to lack of research (on my part).

    And bill thanks for the paint suggestion after further research online Duplicolor looks to be the best plus it has a metal leaf line of paints that will actually mach my bike pretty close (deep royal blue with metal leaf, it came that way).

    Also fun fact on the stock EPA Catalytic exhaust it gets to around 420 degrees Fahrenheit. This is the hottest part of the engine. So yes 500 degree Duplicolor paint will work fine.

    Also because the EPA exhaust has WAY too much back pressure it gets much hotter that it should. That’s why I’m making a custom exhaust with a "tuned to the engine rpm" expansion chamber (also custom).

    (Picture of exhaust coming soon)
     
    #21 recon chris, Jan 21, 2012
    Last edited: Jan 22, 2012
  2. Rocky_Motor

    Rocky_Motor New Member

    Joined:
    Nov 14, 2011
    Messages:
    367
    Likes Received:
    0
    Would you say that high back pressure harms the engine at all?
     
  3. recon chris

    recon chris New Member

    Joined:
    Apr 28, 2011
    Messages:
    87
    Likes Received:
    0
    After tearing the engine completely down and examining it I can honestly say no, not one bit. The way it should harm the engine is by adding extra heat to the jug and the piston. 400 miles later I can honestly say that there is not engine damage due to over backpressure. At first I didn't port the exhaust and it came with the standard "Hole". The engine carb had to be tuned just perfect to get it to run right. Once I semi ported the exhaust pipe to improve flow and lower initial back pressure it became allot less finicky and rode just fine. However the standard EPA exhaust has an end cap and if you take it off you get about another 66cc worth of low end power. You will be able to see it in the pictures what I’m talking about.

    pic of original exhaust
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1264.jpg

    The Catalytic converter in exhaust behind the plate with 5 holes in it (can you say restricted air flow)
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1269.jpg

    What I did to the exhaust pipe port
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1263-1.jpg

    The beginning of the new exhaust that will have only the expansion chamber for precise back pressure, I’m using a 1 inch pipe for the header
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1265.jpg
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1272-1.jpg

    Side by side Old and New
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1261.jpg
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1267-1.jpg
     
    #23 recon chris, Jan 21, 2012
    Last edited: Jan 22, 2012
  4. recon chris

    recon chris New Member

    Joined:
    Apr 28, 2011
    Messages:
    87
    Likes Received:
    0
    Fun facts about the old and the new dimensions on the two exhaust systems.

    Old
    Header inner diameter 17.75mm
    Header outer diameter 20.2mm
    Final exhaust port diameter 10mm

    New
    Header inner diameter 26.2mm
    Header outside diameter 29.6mm
    Final exhaust port diameter N/A
     
  5. recon chris

    recon chris New Member

    Joined:
    Apr 28, 2011
    Messages:
    87
    Likes Received:
    0
    New parts that came in today

    cluch pads, drive sprocket
    [​IMG]
    gasket set
    [​IMG]

    metric english Scale (for crank balancing)
     
    #25 recon chris, Jan 21, 2012
    Last edited: Jan 26, 2012
  6. recon chris

    recon chris New Member

    Joined:
    Apr 28, 2011
    Messages:
    87
    Likes Received:
    0
    So you want to balance a crank hu. Well... it’s easy. You’ll need a scale, drill, lead weight, and a second grade education. You got all that? Then let’s begin.

    (you’ll need a scale for this i got mine at staples 3lb limit accurate to a gram)

    Half way through the crank balancing process right now but the hard part (lol) is over.

    Step one (involving removable fly weight cranks) mach the weight of each fly wheel. There is no reason one weight should be heavier than the other.
    Left side
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1277.jpg
    Right side
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1278.jpg

    Step two to remove the weight from the fly wheel that is heaver evenly, through 3 equally spaced points on the fly wheel, drill holes of the same depth. This will ensure that you’re not setting off the balance of the fly wheel by trimming it down. ALSO! whenever taking weight off by drilling there is always only one face you should drill from and it is the original face that has been drilled at the factory. SECOND DO NOT DRILL A HOLE ALL THE WAY THROUGH THE FLYWEIGHT THIS WILL INCRESE THE VOLUME OF THE CRANK CASE. Although when you bolt the flyweight back onto the crank it will not seal the cavities you have drilled airtight, it will seal it well enough to prevent most air fuel mix from entering during its short compression cycle.

    Before weight matching (red is were im drilling)
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1280.jpg

    After notice three evenly spaced holes (although both flyweights look the same you can see how much material I had to remove to get them to within one gram of each other, thank you china)
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1282.jpg
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1283.jpg

    Step three is to follow the calculations provided by "Big-E" on this forum (http://motorbicycling.com/f13/how-balance-crankshaft-34578-2.html). The instructions he has assumes that you have the ability to take the large end needle bearing and con rod off your crank before you balance it. Since I don’t have a hydraulic press I figured out a way to balance the crank without taking the bearing and con rod off. READ HIS POST PEFORE CONTINUING TO STEP FOUR!

    Step Four- Now that you have read his post and you will have some idea of what I’m talking about do these steps to be able to balance your crank with bearing and con rod attached.

    A. Take the complete weight of the connecting rod small end and the total weight of the piston and rings, piston pin, small end bearing and clips (for me it is 102g)

    To find the weight of the small end of the con rod set it on a scale like this.
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1292.jpg

    B. Multiply the figure (102 grams for me), by your desired balance factor. For arguments sake, I’ll use a mid to high rpm balance factor figure of 57%
    102g. x 0.57= 58.14g.

    { the balance factor is where the engine will hit its smooth balanced sweet spot in the rpm range. Low 50s% will set the sweet spot for low rpm’s were as high 50s to low 60s will have the engine run smoothest a high rpm’s. I’m using 57% as a balance factor because as I accelerate I want the ride to get smoother like a real single cylinder enduro would. However I’m not setting it so high that the sweet spot is unattainable, but it’s up to personal preference were you want the sweet spot to be }

    C. Add the total weight of the large con rod end and large needle bearing to the balance factor figure of "B." 47.4g + 58.14g = 105.54g

    Bob weight to use when balancing the crank shaft at 57% balance factor is 105.54g.

    { There is no way of finding the weight of the large con rod end and the large needle bearing without taking them off the crank. Because "Big-E" was so accurate when he said that the small end con rod and the piston assembly weighed 105 grams (mine weighed 102 grams) I'm going to trust that his measurement for the weight of the large con rod end and the large needle bearing are just as accurate, so for those two parts use the figure 47.4 grams. }

    D. Now at this time you would use the bob weight and attach it to the crank pin WITH THE CON ROD AN NEEDLE BEARING OFF. But because you and I don’t have that luxury how are we going to balance the crank with that pesky unknown weight of the bearing and con rod stuck on there?

    The answer is you do know the weight of the con rod and bearing. First you know the weight of the small end of the con rod (because you measured it properly...right (my con rod small end weighs 35g) and second you know the weight of the large end of the con rod and bearing from "Big-E" 47.4g. So add those two measurements together and you get the total weight of the con rod and large needle bearing. 35g+47.4g=82.4g

    So the con rod and bearing weigh 82.4g. Since it is already perfectly attached to the crank pin you can use it as part of the bob weight. just subtract 82.4g from the bob weight of 105.54g and what is left over is 23.14g.
    105.54g-82.4g=23.14g

    Make a weight that weighs the same as the reaming bob weight but can fit in the small end of the con rod.

    For me I used .22 cal. bullet heads tell I had the correct weight.
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1285.jpg

    Then I melted them down using my striker for my blow torch as a crucible
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1284.jpg

    Then I reweighed them just to make sure
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1286.jpg

    Then I took channel locks and crushed the led weight until it fit in the small end of the con rod


    E. The crank will be balanced when it can be rotated to any orientation without rolling to a heaver weighted side. If, after putting the weight in the small end of the con rod, the rod orientates itself in the down position then you know you have to take weight off the crank pin side of the fly wheel. The opposite applies if the crank pin orientates itself in the up position.

    For me I have to take off more weight on the crank pin side
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1288.jpg

    Just buy luck I know almost exactly how much weight I have to remove because when I remove the bob weight from the con rod it balances perfectly. So take the bob weight, weight and cut the number in half. Then remove that amount of weight from each fly weight (on the crank pin side). for me it should be pretty close to 11g per side but I'm going to start out with 9g a side and work up from there until I get it perfect.

    Pic of it balancing bobless
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1289.jpg

    So this is where I stopped tonight I’ll remove the fly weights and balance it tomorrow.

    Remember although this post is long and may seem complicated I am balancing my crank with nothing more than a scale, drill, lead weight, and elementary math. Read this post a few times if you don’t get it the first time, it will sink in and make sense. (THIS IS EASY)
    dance1
     
    #26 recon chris, Jan 22, 2012
    Last edited: Mar 30, 2012
  7. killercanuck

    killercanuck New Member

    Joined:
    Dec 17, 2009
    Messages:
    1,749
    Likes Received:
    0
    Loving the info, but [​IMG]
     
  8. recon chris

    recon chris New Member

    Joined:
    Apr 28, 2011
    Messages:
    87
    Likes Received:
    0
    I dont know about you guys but the stock "in tank fule filter" just dosn't cut it. So get an inline to go with it.
    [​IMG]
     
    #28 recon chris, Jan 22, 2012
    Last edited: Jan 24, 2012
  9. recon chris

    recon chris New Member

    Joined:
    Apr 28, 2011
    Messages:
    87
    Likes Received:
    0
    I thought i was image taging are the links not visable for everyone?
     
  10. killercanuck

    killercanuck New Member

    Joined:
    Dec 17, 2009
    Messages:
    1,749
    Likes Received:
    0
    Yea, they're clickable, was just being nit-picky about just having the pics show up here :p

    Like so:
    [​IMG]

    Keep up the good work :)
     
  11. Rocky_Motor

    Rocky_Motor New Member

    Joined:
    Nov 14, 2011
    Messages:
    367
    Likes Received:
    0
    The crank is exactly why I am afraid of rebuilding a motor.. You said it's easy, but it just seems to easy to make a mistake and aaah fizzle. Maybe though.. Sometime in the next few months

    I still think it would be cool if someone rebuilt the motors and sold them.
     
    #31 Rocky_Motor, Jan 23, 2012
    Last edited: Jan 23, 2012
  12. recon chris

    recon chris New Member

    Joined:
    Apr 28, 2011
    Messages:
    87
    Likes Received:
    0
    Balancing part 2

    I finally finished balancing the crank. I thought it would take 30 minutes but it took an hour and a half.

    After taking only 6 grams of weight off of both fly weights I went to balance it. It balanced crank pin up without the bob weight (that’s a good sign) then I attached the bob weight and for the most part it was balanced. But trying to be the perfectionist that I am I went "heavy end hunting" for an hour. I must have drilled and weighed that thing 30 times before I felt I got it right. In the last few drill and balance sets I was taking off only tenths of a gram. That is when I had to stop myself and say "that will do pig that will do".

    Here are some picks of the crank after I balanced it tonight, you would be amazed at how much material you have to remove to balance this thing. Believe it or not the entire crank assembly is only 22 grams lighter than when I started but dam does it look like allot of material.

    Before balancing the fly weights
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1290.jpg
    After balancing
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1300.jpg
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1301.jpg
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1303.jpg

    Upgraded the balancing rig to rails instead of setting the crank up on bearings. The bearings have too much resistance for the fine work. However with rails it will drive you crazy because there is so little resistance that you’ll always find a side of your crank that is slightly unbalanced.

    Balanced crank on rails.
    [​IMG]

    If you balance your crank on rails make sure the rails are level if there not the rig will give you false readings
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1296.jpg

    Tomorrows agenda involves properly pressing the bearings back into the magneto side of the crank case. And setting the crank in sed bearing. Then ill be attaching the piston and seeing if I need that piston skirt trimmed or not.

    Please comment and ask questions I love hearing what you guys have to say.
     
    #32 recon chris, Jan 23, 2012
    Last edited: Jan 26, 2012
  13. Cavi Mike

    Cavi Mike New Member

    Joined:
    Dec 17, 2011
    Messages:
    189
    Likes Received:
    0
    That seal has nothing to do with keeping debris out, it's for keeping vacuum in. Without that seal, the engine wouldn't run because it couldn't generate enough vacuum to draw air through the carb, it would just suck air through the bearing.
     
  14. Cavi Mike

    Cavi Mike New Member

    Joined:
    Dec 17, 2011
    Messages:
    189
    Likes Received:
    0
    I also notice you're welding galvanized tubing. You know that releases hexavalent chromium, right? It's a VERY toxic gas.
     
  15. recon chris

    recon chris New Member

    Joined:
    Apr 28, 2011
    Messages:
    87
    Likes Received:
    0
    Cavi Mike... For your fist post you quoted me and added words of your own in there to change the context of my meaning. A sealed bearing has a rubber seal pressing against the inner and outer race track. This is for the purpose of blocking contaminants from entering the bearing.

    “These are the difference between the two bearings I’m using in the engine. One has a metal shield that doesn’t touch the inner raceway and the other has a plastic seal that presses against the outer and inner raceway keeping all dirt out. -recon chris”

    This has nothing to do with the vacuumed affect inside the crank case. I was only talking about the bearing itself.

    Also the point you made that the BEARING makes the seal in the crank case is incorrect. The two bearings in the crank case that came with the engine originally were “open” bearings meaning that they had no seal or shield but were completely open (hence the name). You can literally breath through them I can post pics of them if you need further clarification. However what does make the seal between the crank shaft and the crank case is something called an oil seal. They are spring loaded rubber grommets that press against the inside diameter of the crank case and the outside diameter of the crank shaft. These are located on the outer side of the bearings but is not part of the bearing. You can see it for yourself if you pop your magneto off or if you look behind your pinion gear.

    And yes the electrical conduit I’m using for the exhaust is galvanized and I am welding it. This is something I would not recommend anyone on this forum try by themselves because as you stated mike “releases hexavalent chromium” and that is a toxic gas. However I minimize my risk of exposure to it by taking necessary perceptions (ie. Full face respirator, very well ventilated room, and short stents of welding). Thank you very much for your concern, I am aware of the potential health risks.
     
    #35 recon chris, Jan 23, 2012
    Last edited: Jan 23, 2012
  16. maintenancenazi

    maintenancenazi New Member

    Joined:
    Oct 22, 2011
    Messages:
    157
    Likes Received:
    0
    ^^^ There used to be a guy on here who did just that, but because of some legal issues i believe, he had to stop building them. His name was Chris Hill, you can search his name and see what all he did in rebuilding these engines.
     
  17. recon chris

    recon chris New Member

    Joined:
    Apr 28, 2011
    Messages:
    87
    Likes Received:
    0
    Did a few things tonight

    << POSTED MY FIRST VIDEO ON YOU TUBE FOR YOU GUYS!!!>>

    Finished up with crank washed and cleaned it, applied WD-40 to everything except the screw holes and screws to get rid of any moisture.
    Upgraded the screws from cheese head screws (original) to stainless steel allen head screws.

    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1256-1.jpg

    Applied split washer and a good amount of blue thread locker to each screw before tightening with hand tools. Now that is one happy looking crank!!!

    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1317.jpg

    Here is a way to safely remove the bearing shields without damaging the bearing it self
    First take a knife and gently pry up the shield by twisting the knife not leveraging the knife you’ll break the tip off in the bearing (ask me how I know that)

    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1305.jpg

    Then use needle nose pliers to remove the shield (remember to only remove one shield for each shielded bearing)

    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1306.jpg

    Freeze bearings in a zip lock bag so moisture from the freezer does not come in contact with the freezing bearings

    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1307.jpg

    Now heat one side of the crank case up to 175 or so, not too hot you don’t want to get in danger of warping the case, 175 degrees Fahrenheit is well within the limits of case damage.

    I like to convection cook my cases so the juices stay inside. It will give you a much tenderer ride in the long run :)
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1312.jpg
    http://i1072.photobucket.com/albums/w364/reconchris/CIMG1313.jpg

    Here is a video of how to pressure fit the case bearings read the description for more instructions.
    Remember to do only one side of the case at a time there is no need to rush things.

    Pessing Bearing on 66cc Skyhawk - YouTube

    Hope this simplified the changing bearing process for you guys.
    [​IMG]

    [​IMG]
     
    #37 recon chris, Jan 23, 2012
    Last edited: Jan 26, 2012
  18. recon chris

    recon chris New Member

    Joined:
    Apr 28, 2011
    Messages:
    87
    Likes Received:
    0
    This is really baffling me I installed the crank into one side of the crank case (magneto side) and then installed the new piston with small needle bearing attached. The piston crowns over the top most part of the jug at TDC I don’t remember it being this high before.

    But what really concerns me is that NONE OF THE PORTS ARE EVER FULLY OPEN WHEN ITS THEIR TURN TO BE OPEN!!!
    The worst offenders are the transfer ports that are open at a maximum of 50% of their total port area. Really?…50% why even design the port that big if you are only going to expose 50% of it.

    TDC
    [​IMG]

    Intake
    [​IMG]

    Transfers
    [​IMG]

    Exhaust
    [​IMG]

    Is something way off here or is this normal? I have forgotten what the port alignment was when it had its stock set up. However I haven’t done anything to it that would have changed or thrown off the port alignment. I bought a new piston maybe that’s it? I have put washers between the jug and the crank case to simulate the gasget that is going to go in so i know thats not it.

    So you guys tell me WTF mate?
     
    #38 recon chris, Jan 24, 2012
    Last edited: Jan 25, 2012
  19. Skarrd

    Skarrd Member

    Joined:
    Oct 13, 2010
    Messages:
    499
    Likes Received:
    1
    it's the piston. look at the old and new ones and you'll see the wrist pin is drilled at different heights.

    seems to be a bit of an annoyance with the GT-5 motor, the con rod and piston seem to be a bit unique to it. i've got the same issue with my motor as well.
     
  20. recon chris

    recon chris New Member

    Joined:
    Apr 28, 2011
    Messages:
    87
    Likes Received:
    0
    After measuring both original and new piston there is no difference between the two including the wrist pin hole position on the piston. There is a slight difference in skirt length. The new skirt is about 2mm longer than original. And there is a difference in weight. The old piston weight is 87g and the new one is 83g (that’s a pretty big weight difference for both pistons measuring up almost exactly the same). So (and I cant believe I didn’t think to do this earlier) I installed the old piston and it is the exact same. None of the ports are ever fully open and the piston has the exact same TDC height as the new one. So I guess I was going 30 miles and hour before with half blocked transfer ports and semi blocked intake and exhaust ports.

    WTF CHINA!!

    If they would just mach the jug ports with the piston height (NOT THAT HARD) they would probably get twice the power out of these engines. This isn’t even about Chinese quality control this is just poor engineering. Casting proper ported jugs would cost just as much as casing incorrect ones.

    How am I going to fix this?
    Since all of the bottom ports (exhaust and transfer ports) can benefit from having the piston travel lower so they can be more exposed ill add a thicker seal to the bottom end of the jug. This will raise the jug and better expose the lower ports during BDC.
    However doing this will also lower deck high and therefore lower compression. So to counter that ill sand away some of the top part of the jug. This will make the head bolt on lower on the jug (as opposed to the original) but the thicker jug gaskets on the bottom will keep the piston at the original deck height. The only port that will suffer in all of this will be the intake port but ill shave the piston skirt to make up for that.
    What do you guys think will that work. And if so will it kill bottom end or top end performance? I would think it would give the engine overall more power by greatly improving the efficiency.
     
    #40 recon chris, Jan 24, 2012
    Last edited: Jan 24, 2012

Share This Page